1 Nanoplasmonics: From Present into Future
15
1.2.4.3 Nonlinear Photoprocesses in Nanoplasmonics
As became evident from the first steps of what now is called nanoplasmonics, the
enhanced local fields in resonant metal nanosystems bring about strongly enhanced
nonlinear responses [117–120].
Nonlinear nanoplasmonics is presently a very large and developed field. Some of
its phenomena related to coherent control and spasing are discussed in Sects. 1.4, and
1.5. Here we will give a classification of the nonlinear nanoplasmonic phenomena
and provide some examples, not attempting at being comprehensive.
Nonlinearities in nanoplasmonics can occur in the nanostructured plasmonic
metal, in the embedding medium (dielectric), or in both. Correspondingly, we classify them as intrinsic, extrinsic, or combined. As an independent classification, these
nonlinearities can be classified as weak (perturbative) or strong (nonperturbative).
The perturbative nonlinearities can be coherent (or parametric), characterized by nonlinear polirizabilities [121] and incoherent such as nonlinear absorption, two-photon
fluorescence, surface-enhanced hyper-Raman scattering (SEHRS) [122], nonlinear
photo-modification, two-photon electron emission [123], etc.
Here are some examples illustrating a variety of nonlinear photoprocesses in
nanoplasmonics.
• Second-harmonic generation from nanostructured metal surfaces and metal
nanoparticles [57, 124–132] is a coherent, perturbative (second-order or threewave mixing), intrinsic nonlinearity.
• Enhanced four wave mixing (sum- or difference frequency generation) at metal
surfaces [133] is a coherent, perturbative (third-order or four-wave), intrinsic nonlinearity.
• Another four-wave mixing process in a hybrid plasmonic-photonic waveguide
involves nonlinearities in both metal and dielectric [134] and, therefore, is classified as a coherent, combined, perturbative third-order nonlinear process.
• An all-optical modulator consisting of a plasmonic waveguide covered with CdSe
quantum dots [135] is based on a perturbative third-order, combined nonlinearity.
To the same class belongs a nanoscale-thickness metamaterial modulator [136].
• An ultrafast all-optical modulator using polaritons in an aluminum plasmonic
waveguide is based on perturbative third-order, intrinsic nonlinearity [137]. There
are arguments that this nonlinearity is incoherent, based on interband population
transfer of carriers [137].
• Nonperturbative (strong-field), coherent, extrinsic nonlinearity is plasmonenhanced generation of high harmonics [138] where the enhanced nanoplasmonic
fields excite argon atoms in the surrounding medium. Spaser [31] belongs to the
same class where the nonlinearity is the saturation of the gain medium by the
coherent plasmonic field [139]. The same is true for the loss compensation by gain
[140, 141].
• Intrinsic perturbative nonlinearities in nanoplasmonics stemming from a redistribution of the electron density caused by the ponderomotive forces of nanoplasmonic
fields have been predicted for surface plasmon polaritons [93, 142]. An intrinsic
15
1.2.4.3 Nonlinear Photoprocesses in Nanoplasmonics
As became evident from the first steps of what now is called nanoplasmonics, the
enhanced local fields in resonant metal nanosystems bring about strongly enhanced
nonlinear responses [117–120].
Nonlinear nanoplasmonics is presently a very large and developed field. Some of
its phenomena related to coherent control and spasing are discussed in Sects. 1.4, and
1.5. Here we will give a classification of the nonlinear nanoplasmonic phenomena
and provide some examples, not attempting at being comprehensive.
Nonlinearities in nanoplasmonics can occur in the nanostructured plasmonic
metal, in the embedding medium (dielectric), or in both. Correspondingly, we classify them as intrinsic, extrinsic, or combined. As an independent classification, these
nonlinearities can be classified as weak (perturbative) or strong (nonperturbative).
The perturbative nonlinearities can be coherent (or parametric), characterized by nonlinear polirizabilities [121] and incoherent such as nonlinear absorption, two-photon
fluorescence, surface-enhanced hyper-Raman scattering (SEHRS) [122], nonlinear
photo-modification, two-photon electron emission [123], etc.
Here are some examples illustrating a variety of nonlinear photoprocesses in
nanoplasmonics.
• Second-harmonic generation from nanostructured metal surfaces and metal
nanoparticles [57, 124–132] is a coherent, perturbative (second-order or threewave mixing), intrinsic nonlinearity.
• Enhanced four wave mixing (sum- or difference frequency generation) at metal
surfaces [133] is a coherent, perturbative (third-order or four-wave), intrinsic nonlinearity.
• Another four-wave mixing process in a hybrid plasmonic-photonic waveguide
involves nonlinearities in both metal and dielectric [134] and, therefore, is classified as a coherent, combined, perturbative third-order nonlinear process.
• An all-optical modulator consisting of a plasmonic waveguide covered with CdSe
quantum dots [135] is based on a perturbative third-order, combined nonlinearity.
To the same class belongs a nanoscale-thickness metamaterial modulator [136].
• An ultrafast all-optical modulator using polaritons in an aluminum plasmonic
waveguide is based on perturbative third-order, intrinsic nonlinearity [137]. There
are arguments that this nonlinearity is incoherent, based on interband population
transfer of carriers [137].
• Nonperturbative (strong-field), coherent, extrinsic nonlinearity is plasmonenhanced generation of high harmonics [138] where the enhanced nanoplasmonic
fields excite argon atoms in the surrounding medium. Spaser [31] belongs to the
same class where the nonlinearity is the saturation of the gain medium by the
coherent plasmonic field [139]. The same is true for the loss compensation by gain
[140, 141].
• Intrinsic perturbative nonlinearities in nanoplasmonics stemming from a redistribution of the electron density caused by the ponderomotive forces of nanoplasmonic
fields have been predicted for surface plasmon polaritons [93, 142]. An intrinsic